(CNN) Allergy warning for Pfizer/BioNTech vaccine after UK health workers with allergy history suffer reaction.
This was anticipated, but I did not want to risk being identified as an antivaxer. I would take the Pfizer vaccine, but only in a hospital or well equipped clinic. The presentation of anaphylactic shock is sudden and often severe. Sometimes it requires transfer to an ER. If anaphylactic shock does not occur within the first half hour, it is unlikely to occur, or be severe. mRNA decays rapidly. So unlike the Oxford/Astrazeneca vaccine, the known risk factor is short term.
It is oft said that one cannot be allergic on first exposure to a potential allergen, but there is a big loophole, cross-reactivity of IgE antibodies to a substance with a similar shape.
The synthesis of a class of antibodies is restricted to processes that do not require a lot of energy, and without toxic byproducts. This means that all antibodies of a class are more similar than different. An antibody binds very weakly to the target, like the crummy adhesive of a Post-It note. The bond is so weak, antibodies are constantly falling of their targets. Shape — lock and key — target and antibody, is crucial to the grip.
Since most targets with interesting shapes are proteins, virtually all allergens are proteins, or protein complexes. mRNA, the active constituent of the Pfizer vaccine, is not a protein. Yet RNA is known to be allergenic, meaning that on occasion it can be misidentified as harmful. How can this be?
Proteins are made of small nitrogen containing molecules called amino acids, which can make chains called peptides. If a peptide is long enough, it’s called a protein. RNA is made of nucleobases, which contain sugars, nitrogen-containing compounds and other stuff. The presence of nitrogen is key to molecules with complex, distinctive shapes, a requirement of allergens.
All proteins contain nitrogen, but not all nitrogenous chemicals are proteins. Four different nitrogen-containing nucleobases form long chains that spell the message of life, or in the Pfizer vaccine, instructions to the molecular factories of a human cell for making COVID-19 spike protein, which provokes the immune system to manufacture spike protein antibodies.
Someone or something searching for a shape in the mRNA chain sees randomness unrelated to the purpose of mRNA as a carefully coded message. So it’s practically impossible to identify the cross-reactive region that caused an allergic reaction in a particular patient. But the problem is even worse.
All molecules vibrate. They barely resemble the colorful sticks-and-balls models of illustration. Some molecules are pretty stable. Double-strand DNA is strong enough you could make golf-club shafts out of it. mRNA is the extreme opposite, constantly twisting and gyrating like a crazed break-dancer. Only weighting the ends of the strand with molecular tails, and ultra-cold storage, keep it from tearing apart long enough to reach the patient.
Injected, the mRNA is warmed to body temperature and exposed to hostile enzymes. Quickly vibrating to destruction, mRNA and its fragments present zillions of different, unpredictable shapes to circulating IgE antibodies. A few recipients will be unlucky, with antibodies cross-reactive to this mRNA or its fragments.
The unlucky few can be treated in a well equipped clinic or ER, and the drama will be over in a few hours. If you know how to play the odds, get the Pfizer shot. Better vaccines will come a few months later, but I wouldn’t wait. I would only choose if choice is immediate.